Allow specifying multiple containers in pods

[soenkeliebau]

The agent actively rejects pods that contain more than one container.

Most of the codebase would actually allow multiple containers, but for historic reasons we had this hard limit in place and is has remained ever since.

We should refactor the code to allow multiple containers.

[soenkeliebau]

Not sure how much code that would not support multiple pods is left over, we'd need to investigate this at some point and write a more detailled plan for this issue.

@siegfriedweber